Organic pigments from twisted benzidines

ABSTRACT

Nonmutagenic, highly twisted derivatives of benzidine of the following formula ##STR1## useful as intermediates for the preparation of various organic pigments were obtained. The benzidine derivatives are significantly rotated about the biphenyl linkage due to bulky substituents at the R 2  and/or R 4  positions. Bisazomethine, disaoacetoacetanilide, disazopyrazolone, disazobenzimidazolone and disazonaphthol pigments prepared from these highly twisted benzidines exhibit hypsochromic spectral shifts relative to pigments prepared from other benzidine compounds with less twist about the biphenyl linkage, for instance, other benzidine compounds in which all four R 2  and R 4  represent H. Greenish-yellow, yellow, orange, red and brown pigments obtained from the twisted benzidines are nonmutagenic in the standard Ames test and Prival modification.

TECHNICAL FIELD

The present invention generally relates to intermediates for use in thepreparation of organic pigments. More specifically, this inventionrelates to an approach to the development of novel, nonmutagenicderivatives of benzidine that are highly twisted about the biphenyllinkage and useful for the preparation of organic pigments. A largedihedral angle about the biphenyl linkage, provides for using the novel,nonmutagenic derivatives of benzidine to prepare organic pigments withhypsochromic shifts relative to pigments prepared from derivatives ofbenzidine compounds with a small dihedral angle about the biphenyllinkage.

BACKGROUND OF THE INVENTION

It is well known that bis-chromophoric dyes and pigments (e.g. disazocompounds) prepared from unsubstituted or 3,3'-disubstituted benzidinesexhibit bathochromic spectral shifts relative to identically substitutedmono-chromophoric colorants (e.g. monoazo compounds) prepared fromaniline, or 2-substituted derivatives thereof. For example, in twopapers by Christie et al. (Dyes Pigm., 9 (1988) 37-56; Dyes Pigm., 11(1989) 109-121), a diarylide pigment (see, compound 1) exhibited aλ_(max) of 445 nm in N,N-dimethylformamide (abbreviated as DMF) whilethe corresponding monoarylide pigment (see, compound 2) exhibited aλ_(max) of 392 nm in DMF. ##STR2##

In the case of azo pigments derived from acetoacetanilide, monoarylidepigments (e.g., compound 2) are characterized by good light fastness andpoor solvent resistance. Diarylide pigments (e.g., compound 1), however,possess higher color strength, good thermal stability, and enhancedsolvent resistance compared to the monoarylide pigments. Thus, diarylidepigments are the preferred class of colorants for many applications.

However, the significant bathochromic shift observed when benzidine-typeintermediates are employed in the preparation of diarylide pigments(relative to when aniline-type compounds are used for the synthesis ofmonoarylide pigments) can limit the color gamut of diarylides. Inparticular, greenish-yellow dyes and pigments are not easily accessible.Thus, the ability to prepare colorants based on derivatives of benzidinethat exhibit hypsochromic shifts to those normally achievable isdesirable.

With respect to diarylide and monoarylide pigments, if it is presumedthat diarylides exhibit bathochromic shifts relative to analogousmonoarylides due to, in the most part, significant Π orbital overlapacross the biphenyl linkage at the 1,1'-position, where the numbering ofthe benzidine positions is as follows ##STR3## then, it follows thathypsochromic shifts should be obtainable by decreasing the Π orbitaloverlap.

One method by which a reduction in the degree of Π orbital overlap couldbe achieved is by twisting of the biphenyl group about the 1,1'-bond,for example, by insertion of bulky substituents in the 2,2'-positions.Examination of the open literature (see, for instance, J. Lenoir, TheChemistry of Synthetic Dyes, Volume V, ed. K. Venkataraman, AcademicPress, New York (1952) 345) shows that an example of a diarylide pigmentcontaining a substituent other than hydrogen in the 2,2'-positions hasbeen reported. The example is compound 3 (C.I. Pigment Yellow 15).Compound 4 (C.I. Pigment Yellow 81) and compound 5 (C.I. Pigment Yellow113) are two other examples from the Colour Index (3rd Ed.,Lund-Humphries: London, 1971). See Table 1 below for these threestructures.

                                      TABLE 1                                     __________________________________________________________________________    Selected diarylide pigments derived from twisted benzidines                   1  STR4##                                                                        -                                                                          Compound        R.sub.1 R.sub.2 X.sub.1                                                                              X.sub.2                                                                              X.sub.3                         __________________________________________________________________________    3               OMe     Cl      Me     Me     H                                 4 Cl Cl Me Me H                                                               5 Cl Cl Me Cl H                                                               6 Cl H Me Cl H                                                              __________________________________________________________________________

Compounds 3, 4, and 5 are indeed hypsochromic relative to analogouspigments in which the substituent at each position R₂ is hydrogen. Forinstance, compound 6 (C.I. Pigment Orange 14) is orange, whereascompound 5 is yellow.

Although the inclusion of a bulky substituent into the 2,2'-positions ofbenzidine-type compounds has been undertaken, thereby providing ahypsochromic shift in the resultant colorant, previously made compoundsare believed to be genotoxic, and are therefore potentially hazardous tohumans and the environment. By genotoxic is meant these compoundsinteract with DNA to produce heritable changes in a cell or organism. Inhumans, such changes are associated with birth defects, carcinogenesis,and other types of diseases.

It is well documented in the open literature that benzidine and certainwell-known derivatives of benzidine, for instance,3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine and3,3'-dimethoxybenzidine, hereinafter referred to as common benzidines,are mutagenic. It is also known that certain colorants prepared fromcommon benzidines are mutagenic. Furthermore, it is generally believedthat compounds that exhibit mutagenic activity are potentiallycarcinogenic, and that the manufacture and use of such substancespresents an occupational risk, as well as a potential risk to the healthof living organisms that are exposed to those substances.

Following the discovery of the genotoxicity of benzidine, and later themutagenicity of common benzidines, legislation was introduced in manycountries either banning or severely restricting the industrialproduction and use of these compounds (see, for instance, OSHA.Carcinogens: Occupational Health and Safety Standards; U.S. FederalRegister 39 (1974) 3756-3797, and The Carcinogenic SubstancesRegulations 1967, U.K. Statutory Instrument No. 879). For a discussionof the genotoxicity of benzidine and its congeners, see, for instance,Clarke (Int. Dyer & Text. Printer, No. 5, 250-255) and Fishbein (TheHandbook of Environmental Chemistry, Vol. 3, Part C, Ed. by O.Hutzinger, Springer-Verlag, New York (1984) 1-40).

The restricted synthesis and use of common benzidines has resulted in alarge reduction in their employment in the field of coloration, as wellas other fields such as polymer cross-linking and clinical analysis.Production of high volume dyes based on benzidine itself and itscongeners has been practically discontinued in the Western World.

In certain countries, however, the use of pigments derived from commonbenzidines is permitted, since pigments tend to be unchanged duringnormal processing conditions, and since prolonged exposure of livingorganisms to pigments derived from common benzidines has not been shownto result in significant genotoxicity. Hence, pigments derived fromcommon benzidines, particularly 3,3'-dichlorobenzidine, are stillavailable commercially. In fact, diarylide pigments derived from3,3'-dichlorobenzidine command the major market share of organic yellowpigments.

Nevertheless, the occupational risk remains for manufacturing commonbenzidines themselves prior to their conversion into pigments. There isa risk also of small amounts of common benzidines in their unconvertedform becoming incorporated into pigments, and therefore being releasedinto receiving waters following pigment processing. Furthermore, thereis a risk of common benzidines being released upon thermal degradationof pigments derived from common benzidines following certain processingconditions, such as melt extrusion of pigment-colored polymers.

An examination of the pertinent literature prior to the discovery of thegenotoxicity of benzidine reveals the commercial importance of dyes andpigments prepared from common benzidines. Approximately 250 colorantsderived from benzidine, approximately 90 colorants derived from3,3'-dimethoxybenzidine (o-dianisidine), and approximately 95 colorantsderived from 3,3'-dimethylbenzidine (o-tolidine) are listed in theColour Index (3rd Ed., Lund-Humphries: London, 1971). The commercialimportance of common benzidines was due in part to the economy and easewith which such compounds could be produced, and also to the desirabletechnical properties the aforementioned compounds can impart to acolorant.

In view of the commercial importance of common benzidines prior to thediscovery of their harmful effects to living organisms, the prospectremains that production of such compounds could be restored to themarketplace on a wider scale should a method be found that significantlyreduces the harmful effects of benzidine-type compounds. In recentyears, researchers have worked towards the development of nonmutagenicamines, since mutagenicity is correlated with carcinogenicity. Inaddition, in vitro test methods have been developed to assess themutagenic activity of compounds as a means of predictingcarcinogenicity.

The most widely accepted mutagenicity screening test procedure foramines is the Salmonella mammalian microsome mutagenicity assaydeveloped by Ames et al. (Mutat. Res., 31 (1975) 347), hereinafterreferred to as the Ames test. Subsequently, a modification of the Amestest was introduced by Prival et al. (Mutat. Res., 97 (2) (1982) 103)specifically for evaluating the mutagenicity of azo compounds,hereinafter referred to as the Prival modification. For a generaldiscussion of mutagenicity as it pertains to colored materials, see, forinstance, Freeman et al., Genotoxicity of Azo Dyes: Bases andImplications, Physico-Chemical Principles of Color Chemistry, Advancesin Color Chemistry Series, Vol. 4, ed. by A. T. Peters and H. S. Freeman(Blackie Academic Press: Glasgow, 1996) 254-291; Freeman et al., DyesPigm. 8 (6) (1987) 431-47; and Freeman et al., CHEMTECH, July (1991),438-445.

The discovery by Shahin et al. (Mutation. Res. 79 (1980) 289; Environ.Mutagen. 7 (4) (1985) 535) that the mutagenicity of aromatic amines canbe lowered or removed by incorporating bulky alkyl or alkoxysubstituents ortho to the amino group on a molecule has spurredsignificant interest in this area, particularly for a method to preparenonmutagenic derivatives of benzidine.

In one patent, DE 3 511 544 A1 to Hunger et al., described is thesynthesis of nonmutagenic derivatives of benzidine of the followingformula ##STR5## wherein R represents n-butyl, isopentyl, or phenyl.These compounds were reported to be nonmutagenic in the Ames test,presumably due to the ability of bulky substituents in the two orthopositions to the two amino groups in the 4,4'-positions to preventmetabolic activation.

In another patent, DE 3 511 545 A1 to Hunger et al., described is thesynthesis of derivatives of benzidine of the following formula ##STR6##wherein R represents n-propyl, isopropyl, n-butyl, isobutyl,1-methylpropyl, n-propoxy, isopropoxy, isobutoxy, 1-methylpropoxy, or2-methoxyethoxy. These compounds were reported to be nonmutagenic in theAmes test.

In a later patent, DE 3 534 634 A1 to Bauer et al., nonmutageniccompounds of the type described by Hunger et al. were used asintermediates for the synthesis of water soluble disazo dyes of thefollowing formula ##STR7## wherein R represents groups as described inthe two patents to Hunger et al., and B and B' represent, for instance,substituted naphthalene groups of the following formula ##STR8## whereinX represents, for instance, OH, or NH₂, and n represents 0, 1, or 2.

Furthermore, utilization of a nonmutagenic derivative of benzidine isdescribed in Holland et al. (Tetrahedron, 30, No. 18 (1974) 3299-3302)and also in U.S. Pat. No. 4,211,845 to Conshaw et al. In both instances,a benzidine derivative of the following formula ##STR9## is employed asa reagent for detecting the presence of, for example, glucose in fluids.The compound, 3,5,3',5'-tetramethylbenzidine, is nonmutagenic in theAmes test.

A different approach that has been taken to reduce the occupational riskof colorants derived from benzidines involves the preparation ofdyestuff intermediates that provide technical properties similar to thecommon benzidines, while exhibiting low genotoxicity. An example of thisapproach is shown in U.S. Pat. No. 5,180,817 to Ogino et al., whichdiscloses compounds having, for instance, the following formula##STR10## as replacements for benzidine.

Despite the aforementioned methods for the generation of nonmutagenicderivatives of benzidine, examination of the open literature shows thatbenzidine-type compounds have not been disclosed that contain bulkyalkyl, alkoxy, aryloxy, and/or halogeno substituents ortho to the aminofunctional groups and substituents ortho to the biphenyl linkage, theformer providing nongenotoxicity and the latter also providing colorantsgiving hypsochromic shifts.

SUMMARY AND OBJECTS OF THE INVENTION

Accordingly, the present invention provides a nonmutagenic, highlytwisted benzidine derivative and acid salts thereof, wherein thederivative has (1) two phenyl rings with a biphenyl linkagetherebetween, (2) a first and a second amino functional moiety with thefirst amino moiety on one phenyl ring para to the biphenyl linkage andthe second amino moiety on the other phenyl ring para to the biphenyllinkage, and (3) at least four substituents on the two phenyl rings,wherein the substituents are selected from the group consisting ofalkyl, alkoxy, hydroxyalkyl, alkoxyalkyl, aryloxy, and halogenosubstituents, and mixtures thereof, with (A) one each of two of the samealkyl, alkoxy, hydroxyalkyl, alkoxyalkyl, and aryloxy substituentspresent ortho respectively to each of the two amino functional groups,provided that the alkyl, alkoxy, hydroxyalkyl, and alkoxyalkyl each hasa minimum of three carbons, and (B) one each of two of the same alkyl,alkoxy, hydroxyalkyl, alkoxyalkyl, aryloxy, and halogeno substituentspresent ortho respectively to each side of the biphenyl linkage,provided that the alkyl, alkoxy, hydroxyalkyl, and alkoxyalkyl each hasa maximum of four carbons, and wherein component (A) and component (B)are para to each other for each of the two pairs of component (A) andcomponent (B).

Also, the present invention provides nonmutagenic, highly twistedbenzidine derivatives and acid salts thereof, wherein the benzidinederivatives are of the formula ##STR11## wherein each R₁ is the same andrepresents C₃₋₆ -alkyl, C₃₋₆ -alkoxy, C₃₋₆ -hydroxyalkyl, C₃₋₆-alkoxyalkyl, or aryloxy, and

each R₂ is the same and represents halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy,C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and

each R₃ is the same and represents H or CH₃, and

each R₄ is the same and represents H, halogen, C₁₋₄ -alkyl, C₁₋₄-alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy.

Additionally, the present invention provides for nonmutagenic, highlytwisted colorants represented by the following structures ##STR12##wherein each R₁ is the same and represents C₃₋₆ -alkyl, C₃₋₆ -alkoxy,C₃₋₆ -hydroxyalkyl, C₃₋₆ -alkoxyalkyl, or aryloxy, and

each R₂ is the same and represents halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy,C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and

each R₃ is the same and represents H or CH₃, and

each R₄ is the same and represents H, halogen, C₁₋₄ -alkyl, C₁₋₄-alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and

each X is the same and represents O, S, or NH, and

each X₁ is the same and represents H, CH₃, OCH₃, or halogen, and

each X₂ is the same and represents H, OCH₃, or halogen, and

each X₃ is the same and represents H or halogen, and

each X₄ is the same and represents H or halogen, and

each X₅ is the same and represents H or halogen, and

each X₆ is the same and represents H or halogen.

Hence, two objects of the present invention address simultaneously twoimportant issues pertaining to the chemistry of the class of compoundscommonly referred to as benzidines.

One object is that the nonmutagenic characteristic allows for a decreasein the occupational risk and environmental concern associated with theprior art benzidine-type compounds which has severely limited the scopeof the commercialization of these substances, particularly in the lasttwo decades because the genotoxicity of the prior art benzidine,analogues of benzidine, and certain dyes and pigments preparedtherefrom, has resulted in legislation in many parts of the world eitherbanning or severely limiting their production on a commercial scale.

The other object is that the inventive pigments are more hypsochromicsince, due to the nature of the Π orbital interaction across thebiphenyl linkage of benzidine-type compounds, the pigments prepared fromthe prior art benzidine-type compounds can exhibit wavelengths ofmaximum absorption more bathochromic than desired.

Some of the objects of the invention having been stated above, otherobjects will become evident as the description proceeds, when taken inconnection with the accompanying Laboratory Examples as best describedbelow.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves the incorporation of bulky substituentsin a position ortho to each of the two amino functional groups, as wellas bulky substituents in a position ortho to each side of the biphenyllinkage in the benzidine two-ring system to provide nonmutagenic, highlytwisted benzidine derivatives and compounds made therefrom. The formerincorporation provides for nonmutagenic benzidine-type compounds havinglower occupational and environmental risk. The latter incorporationprovides for benzidine-type compounds that are significantly rotatedabout the biphenyl linkage to reduce Π orbital overlap at this positionand thereby to facilitate the preparation of pigments that are morehypsochromic relative to when, for example, hydrogen occupies thatposition ortho to each side of the biphenyl linkage.

Generally, the nonmutagenic, highly twisted benzidine derivatives andcompounds made therefrom may be any alkyl-substituted,alkoxy-substituted, hydroxyalkyl-substituted, alkoxyalkyl-substituted,or aryloxy-substituted, or a mixture of alkyl, alkoxy, hydroxyalkyl,alkoxyalkyl, or aryloxy and di- or halogeno-substituted benzidinederivatives. In the twisted derivatives and compounds made therefrom,alkyl, alkoxy, hydroxyalkyl, alkoxyalkyl, (each with a minimum of threecarbons), or aryloxy substituents are present ortho to each of the twoamino functional groups, and also, alkyl, alkoxy, hydroxyalkyl,alkoxyalkyl, (each with a maximum of four carbons), or aryloxy, orhalogeno substituents are present ortho to each side of the biphenyllinkage.

It is noted that by the term "highly twisted" as employed herein withrespect to benzidine derivatives and compounds made therefrom, it isintended to mean benzidine derivatives and compounds made therefromsubstituted both ortho to each of the two amino functional groups andortho to each side of the biphenyl linkage.

The selective incorporation of four or more substituents, with two ormore onto each of the rings of the benzidine two-ring system providesnovel, highly twisted benzidine-type compounds that are not onlyoccupationally and environmentally less harmful (i.e., nonmutagenic),but also that are more hypsochromic than many existing, commercializedbenzidine-type compounds.

More specifically, in the preferred embodiment, the present inventionprovides for highly twisted, nonmutagenic benzidine derivatives of thefollowing formula ##STR13## and which are useful as intermediates forthe preparation of organic pigments,

wherein

each R₁ is the same and represents C₃₋₆ -alkyl, C₃₋₆ -alkoxy, C₃₋₆-hydroxyalkyl, C₃₋₆ -alkoxyalkyl, or aryloxy, and

each R₂ is the same and represents halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy,C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and

each R₃ is the same and represents H or CH₃, and

each R₄ is the same and represents H, halogen, C₁₋₄ -alkyl, C₁₋₄-alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy.

In the preferred embodiment, the above derivatives of benzidine arenonmutagenic in the Ames test. Conversely, common benzidines, forexample, 3,3'-dichlorobenzidine, o-dianisidine and o-tolidine, aremutagenic in the Ames test and are regarded as cancer-suspect agents,and are therefore occupationally and environmentally hazardous.

It has been found that the preferred derivatives of benzidine are easilyprepared and purified, and are ideally suited for use as intermediatesin the preparation of organic pigments in which hypsochromic shifts arerequired relative to pigments derived from similarly substitutedbenzidine derivatives but having hydrogens in all four of positions R₂and R₄. Furthermore, due to the ease with which the preferredderivatives of benzidine can be prepared and purified, these compoundsare also logical candidates for use as intermediates in the synthesis ofsoluble organic dyes and in polymer synthesis.

In general, the novel, highly twisted derivatives of benzidine describedabove can be prepared and purified in good yields by a two stageprocedure. First, the hydrazo intermediate can be prepared by reductionof a suitable nitrobenzene derivative, using, for example, a reducingmetal and alkali in either an aqueous or organic medium. Preferably, thereduction is undertaken using zinc and sodium hydroxide in an organicmedium such as ligroine. Second, a benzidine rearrangement of thehydrazo product can be undertaken using aqueous mineral acid solution.

In most cases, the precipitated crude acid salt product, e.g.,dihydrochloride product, can be used directly for the preparation oforganic pigments, following a simple purification procedure, such aswashing with a solvent suitable for removal of impurities withoutdissolving the diamine salt, for instance, bisazomethine,disazoacetoacetanilide, disazopyrazolone, disazobenzimidazolone, anddisazonaphthol pigments.

Thus, the present invention also provides for novel, highly twisted,nonmutagenic organic pigments of following formulae ##STR14## whereineach R₁ is the same and represents C₃₋₆ -alkyl, C₃₋₆ -alkoxy, C₃₋₆-hydroxyalkyl, C₃₋₆ -alkoxyalkyl, or aryloxy, and

each R₂ is the same and represents halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy,C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and

each R₃ is the same and represents H or CH₃, and

each R₄ is the same and represents H, halogen, C₁₋₄ -alkyl, C₁₋₄-alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and

each X is the same and represents O, S, or NH, and

each X₁ is the same and represents H, CH₃, OCH₃, or halogen, and

each X₂ is the same and represents H, OCH₃, or halogen, and

each X₃ is the same and represents H or halogen, and

each X₄ is the same and represents H or halogen, and

each X₅ is the same and represents H or halogen, and

each X₆ is the same and represents H or halogen.

The above novel pigments are nonmutagenic in the Ames test and thePrival modification. As a result, the present invention, in thepreferred embodiment, provides for pigments for which the preparationand use reduces the environmental risk as compared to the environmentalrisk accompanying the preparation and use of prior art colorants. Also,the novel pigments, which are bright greenish-yellow, yellow, orange,red and brown in hue, (more particularly, greenish-yellow and yellow inhue) and which possess high tinctorial strength and high thermalstability, are suitable for use as pigments for inks (printing andwriting), textiles, leather, paper, paints, etc.

Generally, the preparation of the nonmutagenic pigments varies dependingon their chemical structure. For instance, in the case of bisazomethinepigments, an appropriate benzidine derivative is condensed withtriethylorthoformate (abbreviated TEOF) and barbituric acid, or aderivative of the latter, in an organic solvent, such asN,N-dimethylformamide (abbreviated as DMF), at about 120° C., to formthe nonmutagenic pigment, which is isolated by filtration, washed anddried. On the other hand, the synthesis of diarylide, disazopyrazolone,and disazobenzimidazolone pigments involves the tetrazotization of anappropriate benzidine derivative, followed by coupling withacetoacetanilide, 1-phenyl-3-methyl-5-pyrazolone, or5-acetoacetylaminobenzimidazolone, respectively, at 0-20° C., to formthe nonmutagenic pigments, which are isolated by filtration, washed anddried. Additionally, the synthesis of disazonaphthol pigments (referredto as condensed pigments) involves four steps. Aniline-compounds arediazotized and coupled with 3-hydroxy-2-naphthoic acid. The obtaineddiazo colorants are treated in chlorobenzene with SOCl₂ at 40-70° C. andthe resulting monoazo acid chlorides are condensed with an appropriatebenzidine derivative in chlorobenzene at the boiling point to formnonmutagenic pigments, which are isolated by filtration, washed anddried.

More particularly, the present invention provides for the preparation ofnovel highly twisted, nonmutagenic benzidine-type compounds suitable foruse as intermediates in the preparation of organic pigments. The novelbenzidine derivatives are potential replacements for the prior artcommon benzidines, that are known to be mutagenic in vitro andcancer-suspect agents. Also, the novel benzidine derivatives areparticularly useful for the preparation of organic pigments for whichhypsochromic shifts are desired relative to when common benzidines areemployed.

Specific examples of suitable highly twisted derivatives of benzidine,which are nonmutagenic in the Ames test, are as follows

    ______________________________________                                        2  STR15##                                                                    Compound                                                                        number R.sub.1 R.sub.4 R.sub.3 R.sub.2                                      ______________________________________                                         7       n-(CH.sub.2).sub.2 CH.sub.3                                                                 H        H     CH.sub.3                                   8 n-(CH.sub.2).sub.3 CH.sub.3 H H CH.sub.3                                    9 CH(CH.sub.3).sub.2 H H CH.sub.3                                            10 CH.sub.2 CH(CH.sub.3).sub.2 H H CH.sub.3                                   11 CH(CH.sub.3)CH.sub.2 CH.sub.3 H H CH.sub.3                                 12 n-O(CH.sub.2).sub.2 CH.sub.3 H H CH.sub.3                                  13 n-O(CH.sub.2).sub.3 CH.sub.3 H H CH.sub.3                                  14 OCH(CH.sub.3).sub.2 H H CH.sub.3                                           15 OCH.sub.2 CH(CH.sub.3).sub.2 H H CH.sub.3                                  16 OCH(CH.sub.3)CH.sub.2 CH.sub.3 H H CH.sub.3                                17 OPh H H CH.sub.3                                                           18 OCH.sub.2 CH.sub.2 OH H H CH.sub.3                                         19 OCH.sub.2 CH.sub.2 OCH.sub.3 H H CH.sub.3                                  20 CH.sub.3 H CH.sub.3 CH.sub.3                                               21 n-(CH.sub.2).sub.2 CH.sub.3 H H OCH.sub.3                                  22 n-(CH.sub.2).sub.3 CH.sub.3 H H OCH.sub.3                                  23 CH(CH.sub.3).sub.2 H H OCH.sub.3                                           24 CH.sub.2 CH(CH.sub.3).sub.2 H H OCH.sub.3                                  25 CH(CH.sub.3)CH.sub.2 CH.sub.3 H H OCH.sub.3                                26 n-O(CH.sub.2).sub.2 CH.sub.3 H H OCH.sub.3                                 27 n-O(CH.sub.2).sub.3 CH.sub.3 H H OCH.sub.3                                 28 OCH(CH.sub.3).sub.2 H H OCH.sub.3                                          29 OCH.sub.2 CH(CH.sub.3).sub.2 H H OCH.sub.3                                 30 OCH(CH.sub.3)CH.sub.2 CH.sub.3 H H OCH.sub.3                               31 OPh H H OCH.sub.3                                                          32 OCH.sub.2 CH.sub.2 OH H H OCH.sub.3                                        33 OCH.sub.2 CH.sub.2 OCH.sub.3 H H OCH.sub.3                                 34 CH.sub.3 CH.sub.3 H OCH.sub.3                                              35 n-(CH.sub.2).sub.2 CH.sub.3 H H Cl                                         36 n-(CH.sub.2).sub.3 CH.sub.3 H H Cl                                         37 CH(CH.sub.3).sub.2 H H Cl                                                  38 CH.sub.2 CH(CH.sub.3).sub.2 H H Cl                                         39 CH(CH.sub.3)CH.sub.2 CH.sub.3 H H Cl                                       40 n-O(CH.sub.2).sub.2 CH.sub.3 H H Cl                                        41 n-O(CH.sub.2).sub.3 CH.sub.3 H H Cl                                        42 OCH(CH.sub.3).sub.2 H H Cl                                                 43 OCH.sub.2 CH(CH.sub.3).sub.2 H H Cl                                        44 OCH(CH.sub.3)CH.sub.2 CH.sub.3 H H Cl                                      45 OPh H H Cl                                                                 46 OCH.sub.2 CH.sub.2 OH H H Cl                                               47 OCH.sub.2 CH.sub.2 OCH.sub.3 H H Cl                                        48 CH.sub.3 H CH.sub.3 Cl                                                     49 n-(CH.sub.2).sub.2 CH.sub.3 CH.sub.3 H H                                   50 n-(CH.sub.2).sub.3 CH.sub.3 CH.sub.3 H H                                   51 CH(CH.sub.3).sub.2 CH.sub.3 H H                                            52 CH.sub.2 CH(CH.sub.3).sub.2 CH.sub.3 H H                                   53 CH(CH.sub.3)CH.sub.2 CH.sub.3 CH.sub.3 H H                                 54 n-O(CH.sub.2).sub.2 CH.sub.3 CH.sub.3 H H                                  55 n-O(CH.sub.2).sub.3 CH.sub.3 CH.sub.3 H H                                  56 OCH(CH.sub.3).sub.2 CH.sub.3 H H                                           57 OCH.sub.2 CH(CH.sub.3).sub.2 CH.sub.3 H H                                  58 OCH(CH.sub.3)CH.sub.2 CH.sub.3 CH.sub.3 H H                                59 OPh CH.sub.3 H H                                                           60 OCH.sub.2 CH.sub.2 OH CH.sub.3 H H                                         61 OCH.sub.2 CH.sub.2 OCH.sub.3 CH.sub.3 H H                                  62 CH.sub.3 CH.sub.3 CH.sub.3 H                                               63 n-(CH.sub.2).sub.2 CH.sub.3 OCH.sub.3 H H                                  64 n-(CH.sub.2).sub.3 CH.sub.3 OCH.sub.3 H H                                  65 CH(CH.sub.3).sub.2 OCH.sub.3 H H                                           66 CH.sub.2 CH(CH.sub.3).sub.2 OCH.sub.3 H H                                  67 CH(CH.sub.3)CH.sub.2 CH.sub.3 OCH.sub.3 H H                                68 n-O(CH.sub.2).sub.2 CH.sub.3 OCH.sub.3 H H                                 69 n-O(CH.sub.2).sub.3 CH.sub.3 OCH.sub.3 H H                                 70 OCH(CH.sub.3).sub.2 OCH.sub.3 H H                                          71 OCH.sub.2 CH(CH.sub.3).sub.2 OCH.sub.3 H H                                 72 OCH(CH.sub.3)CH.sub.2 CH.sub.3 OCH.sub.3 H H                               73 OPh OCH.sub.3 H H                                                          74 OCH.sub.2 CH.sub.2 OH OCH.sub.3 H H                                        75 OCH.sub.2 CH.sub.2 OCH.sub.3 OCH.sub.3 H H                                 76 CH.sub.3 OCH.sub.3 CH.sub.3 H                                              77 n-(CH.sub.2).sub.2 CH.sub.3 Cl H H                                         78 n-(CH.sub.2).sub.3 CH.sub.3 Cl H H                                         79 CH(CH.sub.3).sub.2 Cl H H                                                  80 CH.sub.2 CH(CH.sub.3).sub.2 Cl H H                                         81 CH(CH.sub.3)CH.sub.2 CH.sub.3 Cl H H                                       82 n-O(CH.sub.2).sub.2 CH.sub.3 Cl H H                                        83 n-O(CH.sub.2).sub.3 CH.sub.3 Cl H H                                        84 OCH(CH.sub.3).sub.2 Cl H H                                                 85 OCH.sub.2 CH(CH.sub.3).sub.2 Cl H H                                        86 OCH(CH.sub.3)CH.sub.2 CH.sub.3 Cl H H                                      87 OPh Cl H H                                                                 88 OCH.sub.2 CH.sub.2 OH Cl H H                                               89 OCH.sub.2 CH.sub.2 OCH.sub.3 Cl H H                                        90 CH.sub.3 Cl CH.sub.3 H                                                   ______________________________________                                    

The key step in all commercial benzidine-type syntheses is therearrangement of the intermediate hydrazo compound to the correspondingbenzidine. This is usually effected using an aqueous mineral acid suchas hydrochloric acid or sulfuric acid. The mechanism for the formationof the benzidine structure from nitrobenzenes has been widely studied,and the following major intermediates (for example, where R=H, Cl, Me,or OMe) are known to form ##STR16##

Therefore, in the present invention, the method of preparation of thenonmutagenic, highly twisted, benzidine derivatives comprises (1)formation of the tetra- or poly-substituted hydrazobenzene intermediateby alkaline reduction of a suitable di- or tri-substituted nitrobenzene,and (2) rearrangement of the hydrazobenzene intermediate using aqueousmineral acid.

In the first stage of the method, reduction of a suitable derivative ofnitrobenzene can be effected in a number of ways, including utilizationof an alkaline medium with zinc or sodium amalgams, zinc metal, or iron.The reduction method employed in the present invention utilized zincdust and sodium hydroxide in an organic solvent chosen from eitherortho-dichlorobenzene, ligroine (boiling range 90-110° C.), or ethanol.

An azobenzene derivative was gradually formed when a reaction vesselcharged with a solution of an alkyl or alkoxy substituted nitrobenzenein, for example, ligroine and zinc was stirred at 70-80° C. and aqueoussodium hydroxide was added dropwise over several hours. The formation ofthe azo intermediate was readily apparent due to the development of ared-orange mixture.

The reduction can then progress further to the hydrazo intermediate, butcommonly required the addition of more zinc, sodium hydroxide and also asmall amount of water. The formation of the hydrazo intermediate can beobserved by utilization of common techniques such as thin layerchromatography (TLC), but it is also indicated by decoloration of thereaction mixture. Once the reaction mixture became colorless, theformation of the hydrazo intermediate was complete and the second stageof the reaction, the benzidine rearrangement, was undertaken.

Following filtration of the reaction mixture, the organic layercontaining the requisite hydrazobenzene intermediate was washed withdilute mineral acid, typically hydrochloric acid. This facilitatedremoval of substituted anilino by-product produced during the reductionof the substituted nitrobenzene.

For the second stage of the method, the hydrazobenzene was then treatedwith aqueous mineral acid, typically 10-40% (weight/weight) aqueoushydrochloric acid at 10-40° C., and the highly twisted, nonmutagenicbenzidine dihydrochloride salt that precipitated was collected byfiltration and purified by standard methods. Standard methods were usedto convert the acid salt to the free base.

The structure and purity of the novel derivatives of benzidine wereconfirmed by proton nuclear magnetic resonance spectroscopy (¹ H NMR),electron impact mass spectrometry (EI MS), and by combustion analysis.

Also, the present invention provides for novel organic pigments(synthesized as described herein) including, but not limited to,bisazomethines, disazoacetoacetanilides (diarylides), disazopyrazolones,disazobenzimidazolones, and disazonaphthols (condensed pigments). Morepreferably, the organic pigment is selected from the followingstructures, where each of R₃ and R₄ is H,

Bisazomethines (bright yellow)

    __________________________________________________________________________    3  STR17##                                                                    Pigment number                                                                            R.sub.1     R.sub.2  X                                            __________________________________________________________________________    91          OCH.sub.2 CH.sub.2 CH.sub.3                                                               CH.sub.3 O                                              92 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 O                                    93 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 S                                     94 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 S                                  __________________________________________________________________________

Diszoacetoacetanilides (yellow to orange)

    __________________________________________________________________________    4  STR18##                                                                    Pigment number R.sub.1   R.sub.2 X.sub.1                                                                              X.sub.2 X.sub.3                       __________________________________________________________________________     95            OCH.sub.2 CH.sub.2 CH.sub.3                                                             CH.sub.3                                                                              H      H       H                                96 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H H H                                97 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 OCH.sub.3 H H                         98 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 OCH.sub.3 H H                        99 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 H OCH.sub.3 H                        100 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H OCH.sub.3 H                       101 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 CH.sub.3 H H                         102 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 CH.sub.3 H H                        103 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 H Cl H                               104 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H Cl H                              105 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 Cl H Cl                              106 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 Cl H Cl                             107 OCH.sub.2 CH.sub.2 CH.sub.3 Cl OCH.sub.3 H H                            __________________________________________________________________________

Disazopyrazolones (orange to reddish-orange)

    __________________________________________________________________________    1  STR19##                                                                    Pigment number       R.sub.1      R.sub.2   X.sub.4                           __________________________________________________________________________    108                  OCH.sub.2 CH.sub.2 CH.sub.3                                                                CH.sub.3  H                                   109 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H                                   110 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 Cl                                   111 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 Cl                                  112 OCH.sub.2 CH.sub.2 CH.sub.3 Cl H                                        __________________________________________________________________________

Disazobenzimidazolones (yellow to orange)

    ______________________________________                                        2  STR20##                                                                    Pigment                                                                         number R.sub.1 R.sub.2                                                      ______________________________________                                        113           OCH.sub.2 CH.sub.2 CH.sub.3                                                              CH.sub.3                                               114 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3                                   ______________________________________                                    

Disazonaphthols (red to brown)

    __________________________________________________________________________    3  STR21##                                                                    Pigment number    R.sub.1     R.sub.2   X.sub.5                                                                              X.sub.6                        __________________________________________________________________________    115               OCH.sub.2 CH.sub.2 CH.sub.3                                                               CH.sub.3  Cl     Cl                               116 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 Cl Cl                             __________________________________________________________________________

Typically, in the case of bisazomethine pigments, the respectivenonmutagenic benzidine derivative was dissolved in DMF, and at roomtemperature TEOF was added, followed by barbituric acid, or a derivativethereof, such as iminobarbituric acid or thiobarbituric acid. Thereaction mixture was then heated gradually to 120° C. and maintained atthis temperature until the reaction was complete. Upon completion ofpigment formation, the reaction mixture was allowed to cool and then wasfiltered. The collected solid was washed, typically with hot methanoland hot water, and dried.

The diarylide, disazopyrazolone and disazobenzimidazolone pigments weresynthesized by tetrazotization of nonmutagenic benzidines with NaNO₂ inthe presence of HCl, followed by coupling of the resulting tetrazoniumsalt with acetoacetanilide, 1-phenyl-3-methyl-5-pyrazolone, or5-acetoacetyloaminobenzimidazolone, respectively. Typically, therespective benzidine hydrochloride or free base was dispersed in anice/water mixture in the presence of HCl. The mixture was stirred at0-5° C. and sodium nitrite solution was added at such a rate to maintaina slight excess of HNO₂. The tetrazotization was continued for 30minutes and the resulting tetrazonium salt was added dropwise at 0-20°C. to the coupling component dispersion, obtained by its dissolution ina H₂ O/NaOH mixture, followed by precipitation with CH₃ COOH/CH₃ COONa(alternatively, with addition of surfactants) at pH=6, at such a ratethat no presence of tetrazo intermediate was observed. The coupling wascontinued for several hours, and after the reaction was completed, thereaction mixture was heated to boiling. The obtained pigments werefiltered hot, washed with hot water and dried.

Disazonaphthol pigments were synthesized via condensation of theappropriate benzidine with a monoazo acid/chloride, obtained by thecoupling reaction of diazotized aniline compound with3-hydroxy-2-naphthoic acid and its chlorination with SOCl₂. Typically,the azo dye was obtained by diazotization of aniline compound with NaNO₂in the presence of HCl, followed by coupling with 3-hydroxy-2-naphthoicacid in the alkaline medium at 0-5° C. The azo dye was isolated byacidification with HCl, washed with water and dried. Dry azo dye wassuspended in dry chlorobenzene and heated to 40° C. Next DMF and SOCl₂were added at this temperature and the reaction mixture was stirred for1 hour. After that time, additional SOCl₂ was added; the temperature wasraised to 70° C. to complete the chlorination step. The acid chloridewas isolated by filtration, washed with chlorobenzene and used forcondensation with the nonmutagenic benzidine derivative. Thecondensation was carried out at the boil in chlorobenzene, and thepigment was isolated by filtration, washed with chlorobenzene and dried.

The structure and purity of each of the various pigments was confirmedby field desorption mass spectroscopy (FDMS), ¹ H-NMR spectroscopy (whenpossible) and combustion analysis.

Mutagenicity testing of the pure derivatives of benzidine was performedusing the standard Ames test, as described by Ames et al. (Mutat. Res.,31 (1975) 347). Mutagenicity testing of the various pigments wasperformed using the standard Ames test, and also using the Privalmodification, as described by Prival et al. (Mutat. Res., 97 (2) (1982)103).

More particularly, two Salmonella typhimurium strains, TA98 and TA100,were employed for mutagenicity testing. All benzidine derivatives andthe pigments made therefrom were evaluated in the presence and absenceof metabolic activation. In the Ames test, metabolic activation wasachieved using rat liver S9, whereas hamster liver S9 was employed inthe Prival modification. A mutagenic response was recorded for a testcompound if the number of revertant colonies counted was more than twicethe number of spontaneous revertant colonies formed in the absence ofthe test compound. A nonmutagenic response (Ames negative or Privalnegative) was recorded when the number of revertant colonies counted wasless than twice the number of spontaneous revertant colonies. All of thetests for the benzidine derivatives and the pigments made therefrom werefound to be nonmutagenic as reported in the Laboratory Examples below.

LABORATORY EXAMPLES

Twisted Benzidine Derivatives

To illustrate how nonmutagenic, highly twisted derivatives of benzidinecan be prepared in accordance with the present invention, the followingExamples set forth methods by which such compounds were produced.

Example 1 Preparation of 2,2'-dimethyl-5,5'-dipropoxybenzidine (compound12) ##STR22##

A solution of 4-methyl-2-nitropropoxybenzene (100.0 g) in ligroine (100ml; boiling range 90-110° C.) was prepared and stirred at 25° C. To thisyellow solution was charged zinc dust (110.6 g). The mixture was stirredand heated to between 70 and 80° C., and 50% aqueous sodium hydroxidesolution (7.4 g) was added dropwise at 70-80° C.

Water (6.5 g) was then added at 70-80° C. The mixture gradually turnedfrom yellow to orange to red.

After several hours, more zinc was charged (20.0 g) and the mixture wasstirred until the organic layer turned colorless. Thin layerchromatography (TLC) was employed to follow the course of the reaction.

When the reaction was complete, the mixture was diluted by theportion-wise addition of ligroine (500 ml; boiling range 90-110° C.),filtered, and the filtrate allowed to cool. The organic layer was thenwashed with aqueous hydrochloric acid solution and then with distilledwater.

The benzidine rearrangement was effected by the dropwise addition of 15%(w/w) aqueous hydrochloric acid (187 g) to the stirred organic layer at20-25° C., and the precipitate was removed by filtration. The crude2,2'-dimethyl-5,5-dipropoxybenzidine dihydrochloride was repeatedlyslurried with acetone and filtered. The crude product was recrystallizedfrom methanol/ethyl acetate. A product yield of 63% was recorded.

For structure confirmation, a portion of the dihydrochloride wasconverted to the free base. The structure of the free base was confirmedby ¹ H NMR, EI MS, and combustion analysis (Theory: C: 73.14, H: 8.59,N: 8.53. Found: C: 73.29, H: 8.65, N: 8.48). Melting point (uncorrected)of the free base was 136° C. Recrystallization of the dihydrochloridesalt was not essential to obtain pure free base . The free base wasfound to be Ames negative .

Example 2 Preparation of 2,2'-dimethoxy-5,5'-dipropoxybenzidine(compound 26) ##STR23##

A solution of 4-methoxy-2-nitropropoxybenzene (100.0 g) in ligroine (100ml) (boiling range 90-110° C.) was prepared and stirred at 25° C. Tothis yellow solution was charged zinc dust (93.0 g). The mixture wasstirred and heated to between 70 and 80° C., and 50% aqueous sodiumhydroxide solution (6.8 g) was added dropwise at 70-80° C. Water (6.0 g)was then added dropwise at 70-80° C. The mixture gradually turned fromyellow to orange to red.

After several hours, more zinc was charged (18.6 g) and the mixture wasstirred until the organic layer turned colorless. Thin layerchromatography (TLC) was employed to follow the course of the reaction.

When the reaction was complete, the mixture was diluted by theportion-wise addition of ligroine (500 ml; boiling range 90-110° C.),filtered, and the filtrate allowed to cool. The organic layer was thenwashed with aqueous hydrochloric acid solution and then with distilledwater.

The benzidine rearrangement was effected by the dropwise addition of 15%(w/w) aqueous hydrochloric acid (172 g) to the stirred organic layer at20-25° C., and the precipitate was removed by filtration. The crude2,2'-dimethoxy-5,5'-dipropoxybenzidine dihydrochloride was slurried withacetone and filtered. The crude product was recrystallized frommethanol/ethyl acetate. A product yield of 53% was recorded.

For structure confirmation, a portion of the dihydrochloride wasconverted to the free base. The structure of the free base was confirmedby ¹ H NMR, EI MS, and combustion analysis (Theory: C: 66.64, H: 7.83,N: 7.77. Found: C: 66.74, H: 7.86, N: 7.83). Melting point (uncorrected)of the free base was 123° C. This product was found to be Ames negative.

Pigments from Twisted Benzidine Derivatives

To illustrate how bisazomethine, diarylide, disazopyrazolone,disazobenzimidazolone, and disazonaphthol pigments derived fromnonmutagenic twisted derivatives of benzidine can be prepared inaccordance with the present invention, the following Examples set forthmethods by which such pigments were produced.

Example 3 Preparation of Pigment 93

Four grams of 2,2'-dimethyl-5,5'-dipropoxybenzidine (from Example 1) wasdissolved in DMF (40 ml), followed by the addition of4,6-dihydroxy-2-mercaptopyrimidine (3.87 g). Next, an additional amountof DMF (40 ml) was added and the reaction mixture was heated to 45° C.until complete solution was obtained.

After 30 minutes, TEOF (4.10 ml) was charged and the reaction mixturewas stirred for several minutes at 25° C. At that point the reactionmixture was heated to 80° C., and after 1 hour the temperature wasraised to 120° C. until the reaction was complete. The reaction mixturewas allowed to cool to 80° C. and the pigment was isolated byfiltration. The solid was stirred with boiling methanol and filteredagain. Next, the colorant was washed with hot water and dried at 40° C.

A product yield of 95% was recorded. FDMS and combustion analysisconfirmed the structure of the greenish-yellow colorant, which wasnegative in both the Ames test and the Prival modification.

Example 4 Preparation of Pigment 95

A suspension of 2,2'-dimethyl-5,5'-dipropoxybenzidine dihydrochloride(4.00 g) (from Example 1) in H₂ O (20 ml), HCl 36% (4 ml) and ice(4.80g) was prepared and stirred for several minutes. To this reactionmixture, at 0-5° C. temperature, NaNO₂ (1.38 g) dissolved in H₂ O (12ml) was added dropwise at such a rate so as to maintain a slight excessof HNO₂. The tetrazotization was continued for 30 minutes, and thenexcess of HNO₂ was decomposed using sulfamic acid. The tetrazonium saltsolution was additionally purified by activated carbon treatment andadded dropwise at 0-5° C. at pH=6 under the surface of a suspension ofacetoacetanilide (3.70 g), obtained by its dissolution in H₂ O (100 ml)containing NaOH (0.64 g), followed by precipitation with HOAc (1.60 ml)and NaOAc.3H₂ O (8.64 g), at such a rate that no presence oftetrazo-intermediate was observed. The coupling reaction was continuedfor several hours and next the reaction mixture was heated to the boil.The pigment was filtered hot, boiled several times with hot water,filtered again, and dried at 40° C.

A product yield of 89% was recorded. FDMS, ¹ H-NMR and combustionanalysis confirmed the structure of the bright yellow pigment, which wasnegative in both the Ames test and the Prival modification.

Example 5 Preparation of Pigment 108

The tetrazonium component was prepared by the method described inExample 4 and added dropwise at 0-5° C., at pH=6 to a suspension of1-phenyl-3-methyl-5-pyrazolone (3.48 g) obtained by its dissolution inH₂ O (100 ml) with NaOH (0.64 g), followed by precipitation with HOAc(1.60 ml) and NaOAc.3H₂ O (8.64 g). The coupling reaction was carriedout in the way described in Example 4. The pigment was hot filtered,washed with hot water several times and dried in the oven at 40° C.

A product yield of 75% was recorded. FDMS, ¹ H-NMR and combustionanalysis confirmed the structure of the bright orange pigment, which wasnegative in both the Ames test and the Prival modification.

Example 6 Preparation of Pigment 113

The tetrazonium component was prepared in the way described in Example 4and added dropwise at 20° C. at pH=6 to a suspension of5-acetoacetylaminobenzimidazolone (4.90 g). This suspension was preparedin the way described in Example 4, followed by the addition of a smallamount of Surfarynol and Triton X-100. The pigment was isolated in theway described in Example 4 and dried at 40° C. Then, dry pigment wasboiled with DMF for several minutes. After cooling to 50° C., thepigment was collected by filtration, washed with water, and dried at 40°C.

A product yield of 85% was recorded. FDMS and combustion analysisconfirmed the structure of the bright yellow pigment, which was negativein both the Ames test and the Prival modification.

Example 7 Preparation of Pigment 115

A mixture of 2,5-dichloroaniline (8.10 g) in H₂ O (50 ml) and 30% HCl(15 ml) was heated at 60° C. for several minutes. Next ice was added,and at 0-2° C. the reaction mixture was treated with NaNO₂ (3.45 g)dissolved in H₂ O (15 ml). The diazotization was continued for severalminutes, followed by filtration of a small amount of solid. Thediazonium salt was added dropwise to 3-hydroxy-2-naphthoic acid (10 g)dissolved in H₂ O (200 ml) containing 30% NaOH (5 ml) and Na₂ CO₃ (17 g)at such a rate so as to maintain the temperature at 0-2° C. The couplingwas continued until it was complete.

The monoazo dye was isolated by acidification with 30% HCl filtered,washed with water and dried at 40° C. The resulting monoazo dye wasdispersed in dry chlorobenzene and heated to 40° C. To this mixture, DMF(0.5 ml) and SOCl₂ (2.5 ml) were added and the chlorination wascontinued for 1 hour. Then, additional SOCl₂ (2 ml) was added; thetemperature was raised to 70° C.; and the reaction mixture was stirredfor 2 hours. The resulting acid chloride was filtered and washed withchlorobenzene. Next, it was dispersed again in dry chlorobenzene andadded to a solution of 2,2'-dimethyl-5,5'-dipropoxybenzidine (6.68 g) inchlorobenzene at 70° C. The reaction mixture was then heated to boilingand held there until the condensation was complete. The pigment wasfiltered hot, washed with chlorobenzene and dried at 40° C.

A product yield of 70% was recorded. FDMS and combustion analysisconfirmed the structure of the bright red pigment, which was negative inboth the Ames test and the Prival modification.

Example 8 Preparation of Pigment 98

A suspension of 2,2'-dimethoxy-5,5'-dipropoxybenzidine (4.00 g) in H₂ O(16 ml), HCl 36% (6 ml) and ice (4.80 g) was prepared and stirred forseveral minutes. To this reaction mixture, at 0-5° C., NaNO₂ (1.54 g)dissolved in H₂ O (16 ml) was added dropwise at a rate so as to maintaina slight excess of HNO₂. Tetrazotization was continued for severalminutes, and excess HNO₂ was decomposed using sulfamic acid. Thetetrazonium salt solution was additionally purified using activatedcarbon, and added dropwise at 0-5° C. and pH=6, under the surface of asuspension of acetoacetanilide (4.11 g), obtained by its dissolution inH₂ O containing NaOH (0.76 g), followed by precipitation with HOAc (1.91ml) and NaOAc.3H₂ O (10.35 g) at which point the tetrazo intermediatewas consumed. The coupling reaction was continued for several hours andthen the reaction mixture was heated to the boil. The pigment wasfiltered hot, boiled several times in hot water, filtered hot again, anddried at 40° C.

A product yield of 58.5% was recorded. FDMS, ¹ H-NMR and combustionanalysis confirmed the structure of the yellow-orange pigment, which wasnegative in both the Ames test and Prival modification.

Example 9 Preparation of Pigment 107

A suspension of 2,2'-dichloro-5,5'-dipropoxybenzidine dihydrochloride(4.00 g) in H₂ O (3.75 ml), HCl 36% (4.00 ml) and ice (4.80 g) wasprepared and stirred for several minutes. To this reaction mixture, at0-5° C., NaNO₂ (1.48 g) dissolved in H₂ O (12 ml) was added dropwise ata rate so as to maintain a slight excess of HNO₂.

Tetrazotization was continued for 30 minutes, and then excess HNO₂ wasdecomposed using sulfamic acid. The tetrazonium salt solution wasadditionally purified using activated carbon and added dropwise at 0-5°C. and pH=6, under the surface of suspension of o-acetoacetaniside (4.44g), obtained by its dissolution in H₂ O containing NaOH (0.68 g),followed by precipitation from HOAc (1.60 ml) and NaOAC.3H₂ O (8.82 g)at which point the tetrazo intermediate was consumed. The couplingreaction was continued for several hours and then the reaction mixturewas heated to the boil. The pigment was filtered hot, boiled severaltimes in hot water, filtered hot again, and dried at 40° C.

A product yield of 62.5% was recorded. FDMS, ¹ H-NMR and combustionanalysis confirmed the structure of the yellow pigment, which wasnegative in both the Ames test and the Prival modification.

It will be understood that various details of the present invention maybe changed without departing from the spirit and scope of the invention.Furthermore, the foregoing examples are for illustrative purposes only,and in no way are intended to limit the scope of the invention asdefined by the claims.

What is claimed is:
 1. A nonmutagenic, highly twisted benzidine compoundor acid salts thereof, wherein the benzidine compound or acid saltsthereof have (1) two phenyl rings with a biphenyl linkage therebetween,and (2) a first and a second amino functional moiety with the firstamino moiety on one phenyl ring para to the biphenyl linkage and thesecond amino moiety on the other phenyl ring para to the biphenyllinkage, and (3) at least four substituents on the two phenyl rings,wherein the substituents are selected from the group consisting ofalkyl, alkoxy, hydroxyalkyl, alkoxyalkyl, aryloxy, and halogenosubstituents, and mixtures thereof, with(A) one each of two of the samealkyl, alkoxy, hydroxyalkyl, alkoxyalkyl, and aryloxy substituentspresent ortho respectively to each of the two amino functional groups,provided that the alkyl, alkoxy, hydroxyalkyl, and alkoxyalkyl each hasa minimum of three carbons, and (B) one each of two of the same alkyl,alkoxy, hydroxyalkyl, alkoxyalkyl, aryloxy, and halogeno substituentspresent ortho respectively to each side of the biphenyl linkage,provided that the alkyl, alkoxy, hydroxyalkyl, and alkoxyalkyl each hasa maximum of four carbons,and wherein (A) and (B) are para to each otherfor each of the two pairs of (A) and (B).
 2. The nonmutagenic, highlytwisted compound or benzidine and acid salts thereof according to claim1, wherein the benzidine compound has the formula ##STR24## wherein eachR₁ is the same and is a substituent selected from the group consistingof C₃₋₆ -alkyl, C₃₋₆ -alkoxy, C₃₋₆ -hydroxyalkyl, C₃₋₆ alkoxyalkyl, andaryloxy, andeach R₂ is the same and is a substituent selected from thegroup consisting of halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy, C₁₋₄-hydroxyalkyl, C₁₋₄ -alkoxyalkyl, and aryloxy, and each R₃ is the sameand is a substituent selected from the group consisting of H, and CH₃,and each R₄ is the same and is a substituent selected from the groupconsisting of H, halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy, C₁₋₄ -hydroxyalkyl,C₁₋₄ -alkoxyalkyl, and aryloxy.
 3. The benzidine compound or and acidsalts thereof according to claim 2, wherein the benzidine compound isselected from the group consisting of compounds 7 through 90, where eachof R₁, R₂, R₃, and R₄ is defined as follows:

    ______________________________________                                        Compound                                                                        number R.sub.1 R.sub.4 R.sub.3 R.sub.2                                      ______________________________________                                         7       n-(CH.sub.2).sub.2 CH.sub.3                                                                 H        H     CH.sub.3                                   8 n-(CH.sub.2).sub.3 CH.sub.3 H H CH.sub.3                                    9 CH(CH.sub.3).sub.2 H H CH.sub.3                                            10 CH.sub.2 CH(CH.sub.3).sub.2 H H CH.sub.3                                   11 CH(CH.sub.3)CH.sub.2 CH.sub.3 H H CH.sub.3                                 12 n-O(CH.sub.2).sub.2 CH.sub.3 H H CH.sub.3                                  13 n-O(CH.sub.2).sub.3 CH.sub.3 H H CH.sub.3                                  14 OCH(CH.sub.3).sub.2 H H CH.sub.3                                           15 OCH.sub.2 CH(CH.sub.3).sub.2 H H CH.sub.3                                  16 OCH(CH.sub.3)CH.sub.2 CH.sub.3 H H CH.sub.3                                17 OPh H H CH.sub.3                                                           18 OCH.sub.2 CH.sub.2 OH H H CH.sub.3                                         19 OCH.sub.2 CH.sub.2 OCH.sub.3 H H CH.sub.3                                  20 CH.sub.3 H CH.sub.3 CH.sub.3                                               21 n-(CH.sub.2).sub.2 CH.sub.3 H H OCH.sub.3                                  22 n-(CH.sub.2).sub.3 CH.sub.3 H H OCH.sub.3                                  23 CH(CH.sub.3).sub.2 H H OCH.sub.3                                           24 CH.sub.2 CH(CH.sub.3).sub.2 H H OCH.sub.3                                  25 CH(CH.sub.3)CH.sub.2 CH.sub.3 H H OCH.sub.3                                26 n-O(CH.sub.2).sub.2 CH.sub.3 H H OCH.sub.3                                 27 n-O(CH.sub.2).sub.3 CH.sub.3 H H OCH.sub.3                                 28 OCH(CH.sub.3).sub.2 H H OCH.sub.3                                          29 OCH.sub.2 CH(CH.sub.3).sub.2 H H OCH.sub.3                                 30 OCH(CH.sub.3)CH.sub.2 CH.sub.3 H H OCH.sub.3                               31 OPh H H OCH.sub.3                                                          32 OCH.sub.2 CH.sub.2 OH H H OCH.sub.3                                        33 OCH.sub.2 CH.sub.2 OCH.sub.3 H H OCH.sub.3                                 34 CH.sub.3 CH.sub.3 H OCH.sub.3                                              35 n-(CH.sub.2).sub.2 CH.sub.3 H H Cl                                         36 n-(CH.sub.2).sub.3 CH.sub.3 H H Cl                                         37 CH(CH.sub.3).sub.2 H H Cl                                                  38 CH.sub.2 CH(CH.sub.3).sub.2 H H Cl                                         39 CH(CH.sub.3)CH.sub.2 CH.sub.3 H H Cl                                       40 n-O(CH.sub.2).sub.2 CH.sub.3 H H Cl                                        41 n-O(CH.sub.2).sub.3 CH.sub.3 H H Cl                                        42 OCH(CH.sub.3).sub.2 H H Cl                                                 43 OCH.sub.2 CH(CH.sub.3).sub.2 H H Cl                                        44 OCH(CH.sub.3)CH.sub.2 CH.sub.3 H H Cl                                      45 OPh H H Cl                                                                 46 OCH.sub.2 CH.sub.2 OH H H Cl                                               47 OCH.sub.2 CH.sub.2 OCH.sub.3 H H Cl                                        48 CH.sub.3 H CH.sub.3 Cl                                                     49 n-(CH.sub.2).sub.2 CH.sub.3 CH.sub.3 H H                                   50 n-(CH.sub.2).sub.3 CH.sub.3 CH.sub.3 H H                                   51 CH(CH.sub.3).sub.2 CH.sub.3 H H                                            52 CH.sub.2 CH(CH.sub.3).sub.2 CH.sub.3 H H                                   53 CH(CH.sub.3)CH.sub.2 CH.sub.3 CH.sub.3 H H                                 54 n-O(CH.sub.2).sub.2 CH.sub.3 CH.sub.3 H H                                  55 n-O(CH.sub.2).sub.3 CH.sub.3 CH.sub.3 H H                                  56 OCH(CH.sub.3).sub.2 CH.sub.3 H H                                           57 OCH.sub.2 CH(CH.sub.3).sub.2 CH.sub.3 H H                                  58 OCH(CH.sub.3)CH.sub.2 CH.sub.3 CH.sub.3 H H                                59 OPh CH.sub.3 H H                                                           60 OCH.sub.2 CH.sub.2 OH CH.sub.3 H H                                         61 OCH.sub.2 CH.sub.2 OCH.sub.3 CH.sub.3 H H                                  62 CH.sub.3 CH.sub.3 CH.sub.3 H                                               63 n-(CH.sub.2).sub.2 CH.sub.3 OCH.sub.3 H H                                  64 n-(CH.sub.2).sub.3 CH.sub.3 OCH.sub.3 H H                                  65 CH(CH.sub.3).sub.2 OCH.sub.3 H H                                           66 CH.sub.2 CH(CH.sub.3).sub.2 OCH.sub.3 H H                                  67 CH(CH.sub.3)CH.sub.2 CH.sub.3 OCH.sub.3 H H                                68 n-O(CH.sub.2).sub.2 CH.sub.3 OCH.sub.3 H H                                 69 n-O(CH.sub.2).sub.3 CH.sub.3 OCH.sub.3 H H                                 70 OCH(CH.sub.3).sub.2 OCH.sub.3 H H                                          71 OCH.sub.2 CH(CH.sub.3).sub.2 OCH.sub.3 H H                                 72 OCH(CH.sub.3)CH.sub.2 CH.sub.3 OCH.sub.3 H H                               73 OPh OCH.sub.3 H H                                                          74 OCH.sub.2 CH.sub.2 OH OCH.sub.3 H H                                        75 OCH.sub.2 CH.sub.2 OCH.sub.3 OCH.sub.3 H H                                 76 CH.sub.3 OCH.sub.3 CH.sub.3 H                                              77 n-(CH.sub.2).sub.2 CH.sub.3 Cl H H                                         78 n-(CH.sub.2).sub.3 CH.sub.3 Cl H H                                         79 CH(CH.sub.3).sub.2 Cl H H                                                  80 CH.sub.2 CH(CH.sub.3).sub.2 Cl H H                                         81 CH(CH.sub.3)CH.sub.2 CH.sub.3 Cl H H                                       82 n-O(CH.sub.2).sub.2 CH.sub.3 Cl H H                                        83 n-O(CH.sub.2).sub.3 CH.sub.3 Cl H H                                        84 OCH(CH.sub.3).sub.2 Cl H H                                                 85 OCH.sub.2 CH(CH.sub.3).sub.2 Cl H H                                        86 OCH(CH.sub.3)CH.sub.2 CH.sub.3 Cl H H                                      87 OPh Cl H H                                                                 88 OCH.sub.2 CH.sub.2 OH Cl H H                                               89 OCH.sub.2 CH.sub.2 OCH.sub.3 Cl H H                                        90 CH.sub.3 Cl CH.sub.3 H                                                   ______________________________________                                    

for each respective compound 7 through
 90. 4. The benzidine compound orand acid salts thereof according to claim 3, wherein the benzidinecompound is selected from the group consisting of2,2'-dimethyl-5,5'-dipropoxybenzidine and2,2'-dimethoxy-5,5'-dipropoxybenzidine.
 5. The benzidine compound or andacid salts thereof according to claim 2, wherein the benzidine compoundor and acid salts thereof are nonmutagenic in accordance with the Amestest.
 6. A method of making a nonmutagenic, highly twisted benzidinecompound or acid salts thereof, wherein the benzidine compound has theformula ##STR25## wherein each R₁ is the same and is a substituentselected from the group consisting of C₃₋₆ -alkyl, C₃₋₆ -alkoxy, C₃₋₆-hydroxyalkyl, C₃₋₆ -alkoxyalkyl, and aryloxy, andeach R₂ is the sameand is a substituent selected from the group consisting of halogen, C₁₋₄-alkyl, C₁₋₄ -alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, andaryloxy, and each R₃ is the same and is a substituent selected from thegroup consisting of H and CH₃, and each R₄ is the same and is asubstituent selected from the group consisting of H, halogen, C₁₋₄-alkyl, C₁₋₄ -alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, andaryloxy, the method comprising (1) forming a correspondingly substitutedhydrazobenzene intermediate by alkaline reduction of a suitablysubstituted nitrobenzene and (2) rearranging the resultinghydrazobenzene intermediate with acid.
 7. A nonmutagenic pigmentprepared from a nonmutagenic, highly twisted benzidine compound or acidsalts thereof, wherein the benzidine compound or acid salts thereof have(1) two phenyl rings with a biphenyl linkage therebetween, (2) a firstand a second amino functional moiety with the first amino moiety on onephenyl ring para to the biphenyl linkage and the second amino moiety onthe other phenyl ring para to the second amino moiety on the otherphenyl ring para to the biphenyl linkage, and (3) at least foursubstituents on the two phenyl rings, wherein the substituents areselected from the group consisting of alkyl, alkoxy, hydroxyalkyl,alkoxyalkyl, aryloxy, and halageno substituents, and mixtures thereof,with(A) one each of two of the same alkyl, alkoxy, hydroxyalkyl,alkoxyalkyl, and aryloxy substituents present ortho respectively to eachof the two amino functional groups, provided that the alkyl, alkoxy,hydroxyalkyl, and alkoxyalkyl each has a minimum of three carbons, and(B) one each of two of the same alkyl, alkoxy, hydroxyalkyl,alkoxyalkyl, aryloxy, and halogeno substituents present orthorespectively to each side of the biphenyl linkage, provided that thealkyl, alkoxy, hydroxyalkyl, and alkoxyalkyl each has a maximum of fourcarbons,and wherein (A) and (B) are para to each other for each of thetwo pairs of (A) and (B).
 8. The pigment according to claim 7, whereinthe pigment is prepared from a nonmutagenic, highly twisted benzidinecompound or acid salts thereof, wherein the benzidine compound has theformula ##STR26## wherein each R₁ is the same and is a substituentselected from the group consisting of C₃₋₆ -alkyl, C₃₋₆ -alkoxy, C₃₋₆-hydroxyalkyl, C₃₋₆ -alkoxyalkyl, and aryloxy, andeach R₂ is the sameand is a substituent selected from the group consisting of halogen, C₁₋₄-alkyl, C₁₋₄ -alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, andaryloxy, and each R₃ is the same and is a substituent selected from thegroup consisting of H and CH₃, and each R₄ is the same and is asubstituent selected from the group consisting of H, halogen, C₁₋₄-alkyl, C₁₋₄ -alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄ -alkoxyalkyl, andaryloxy.
 9. The pigment according to claim 8, wherein the pigment isselected from the group consisting of bisazomethines,disazoacetoacetanalides, disazopyrazolones, disazobenzimidazolones, anddisazonaphthols.
 10. The pigment according to claim 9, wherein thepigment is selected from the group consisting of pigments 91 through116, where each of R₃ and R₄ is H, and each of R₁, R₂, X, X₁, X₂, X₃,X₄, X₅, and X₆ is defined as follows:Bisazomethines (bright yellow)

    __________________________________________________________________________    4  STR27##                                                                    Bisazomethines (bright yellow)                                                Pigment number       R.sub.1      R.sub.2    X                                __________________________________________________________________________       91 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 O                                     92 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 O                                    93 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 S                                     94 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 S                                 __________________________________________________________________________    5  STR28##                                                                       -                                                                          Disazoacetoacetanilides (yellow to orange)                                    Pigment number                                                                             R.sub.1    R.sub.2 X.sub.1                                                                              X.sub.2 X.sub.3                        __________________________________________________________________________       95 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 H H H                                 96 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H H H                                97 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 OCH.sub.3 H H                         98 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 OCH.sub.3 H H                        99 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 H OCH.sub.3 H                        100 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H OCH.sub.3 H                       101 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 CH.sub.3 H H                         102 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 CH.sub.3 H H                        103 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 H Cl H                               104 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H Cl H                              105 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 Cl H Cl                              106 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 Cl H Cl                             107 OCH.sub.2 CH.sub.2 CH.sub.3 Cl OCH.sub.3 H H                            __________________________________________________________________________

Disazopyrazolones (orange to reddish-orange)

    __________________________________________________________________________    1  STR29##                                                                    Pigment number      R.sub.1      R.sub.2   X.sub.4                            __________________________________________________________________________    108                 OCH.sub.2 CH.sub.2 CH.sub.3                                                                CH.sub.3  H                                    109 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 H                                   110 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 Cl                                   111 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 Cl                                  112 OCH.sub.2 CH.sub.2 CH.sub.3 Cl H                                        __________________________________________________________________________

Disazobenzimidazolones (yellow to orange)

    __________________________________________________________________________    2  STR30##                                                                    Disazobenzimidazolones (yellow to orange)                                     Pigment number            R.sub.1         R.sub.2                             __________________________________________________________________________      113 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3                                      114 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3                                   __________________________________________________________________________    3  STR31##                                                                       -                                                                          Disazonaphthols (red to brown)                                                Pigment number     R.sub.1     R.sub.2  X.sub.5                                                                              X.sub.6                        __________________________________________________________________________      115 OCH.sub.2 CH.sub.2 CH.sub.3 CH.sub.3 Cl Cl                                116 OCH.sub.2 CH.sub.2 CH.sub.3 OCH.sub.3 Cl Cl                             __________________________________________________________________________

for each respective pigment 91 through
 116. 11. The pigment according toclaim 8, wherein the pigment is nonmutagenic in accordance with the Amestest and the Prival modification of the Ames test.
 12. The pigmentaccording to claim 8, wherein the pigment exhibits a color selected fromthe group consisting of greenish-yellow, yellow, orange, red, brown, andcombinations thereof.
 13. A method of making a nonmutagenic pigmentwherein the pigment has a formula selected from the group consisting of##STR32## wherein each R₁ is the same and represents C₃₋₆ -alkyl, C₃₋₆-alkoxy, C₃₋₆ -hydroxyalkyl, C₃₋₆ -alkoxyalkyl, or aryloxy, andeach R₂is the same and represents halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy, C₁₋₄-hydroxyalkyl, C₁₋₄ -alkoxyalkyl, or aryloxy, and each R₃ is the sameand represents H or CH₃, and each R₄ is the same and represents H,halogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy, C₁₋₄ -hydroxyalkyl, C₁₋₄-alkoxyalkyl, or aryloxy, and each X is the same and represents O, S, orNH, and each X₁ is the same and represents H, CH₃, OCH₃, or halogen, andeach X₂ is the same and represents H, OCH₃, or halogen, and each X₃ isthe same and represents H or halogen, and each X₄ is the same andrepresents H or halogen, and each X₅ is the same and represents H orhalogen, and each X₆ is the same and represents H or halogen, saidmethod comprising:a. providing a corresponding nonmutagenic, highlytwisted benzidine compound or acid salts thereof, wherein the benzidinecompound has the formula ##STR33## and the benzidine compound or acidsalts thereof are correspondingly substituted with the same R₁, R₂, R₃,and R₄, and b. reacting the nonmutagenic benzidine compound or acidsalts thereof with an agent, that substitutes on each N of thenonmutagenic benzidine compound or acid salts thereof, one of each oftwo of the same moieties, where each moiety has the same X, X₁, X₂, X₃,X₄, X₅, and X₆, and therefore that converts the nonmutagenic benzidinecompound or acid salts thereof to the corresponding nonmutagenic pigmentthat is correspondingly substituted with the same R₁, R₂, R₃, R₄, X, X₁,X₂, X₃, X₄, X₅, and X₆.
 14. The method of claim 13, wherein the formulais for bisazomethine pigments, and the agent is a formylating agent inthe presence of an acid.
 15. The method of claim 13, wherein thebenzidine compound or acid salts thereof are first tetrazotized prior toreacting with the agent; and the formula is for pigments selected fromthe group consisting of disazoacetoacetanalides, disazopyrazolones, anddisazobenzimidazolones; and the agent is a coupling agent selected fromthe group consisting of acetoacetanilide,1-phenyl-3-methyl-5-pyrazolone, and 5-acetoacetylamino-benzimidazolone,respectively.
 16. The method of claim 13, wherein the formula is fordiazonaphthol pigments, and the agent is an aniline compound diazotizedand coupled with 3-hydroxy-2-naphthoic acid followed by chlorination.